The present disclosure is directed to airflow measuring devices. More particularly, it is directed to an airflow sensor housing used to measure mass airflow in internal combustion engines.
It has been considered important to measure the flow of mass air inducted into an internal combustion engine, in order to control the air to fuel ratio of the engine. Accurate measurement of airflow is important for correctly monitoring engine parameters and emission controls. To comply with emission requirements for motor vehicles, a specific air fuel ratio must be precisely maintained. This requires the use of sensors which accurately record the actual air mass flow and output this information in the form of electrical signals to the control electronics of the engine. A mass airflow sensor provides information necessary for the engine control unit to balance and deliver the correct fuel mass to the engine. The mass airflow sensor is located in the intake air stream and measures the mass of air entering the engine.
Two known types of mass airflow sensors used for this purpose are vane meter sensors and hot wire sensors. Hot wire mass airflow sensors are now more common. In such a sensor, the wire is so positioned that the air flowing to the engine flows around the wire. As airflows past the wire, it cools, decreasing its resistance. This allows more current to flow through the circuit or causes a smaller voltage drop over the wire, depending on whether the system employs constant voltage over the wire or constant current through the wire. The current or voltage drop is proportional to the mass of air flowing past the wire. An integrated electronic circuit converts the measurement into a calibrated signal which is sent to the engine control unit of the internal combustion engine. Air mass flow in the internal combustion engine is measured along with atmospheric pressure and air temperature so that the quantity of fuel injected can be calibrated to the current power requirements of the engine.
Precise measurement of airflow is not only important in modern engine control systems but also in testing systems. It is known to mount a mass airflow sensor directly on a main venturi member of an air intake system employed for an internal combustion engine. The main venturi member has a bypass passage connected at its downstream end to a low pressure region connected at the narrowed portion of the venturi. The sensing elements of the mass airflow sensor are disposed in this bypass passage and measure airflow therethrough.
It is also known to mount an airflow sensor directly to a sensor housing, which forms part of the air intake or air induction system of an internal combustion engine, with the sensor housing having a main airflow passageway and a smaller diameter airflow passageway offset to one side of the main passageway. The sensing head of a mass airflow sensor can extend into the smaller diameter airflow channel and detect airflow therethrough.
Both of these known systems have disadvantages in that they cannot be adapted to accurately measure airflow in larger sized internal combustion engines. Present airflow measurement systems for engines are limited by size, accuracy and signal noise. Difficulties occur in accurately measuring mass airflow in larger internal combustion engines. For example, larger commercial engines for engine control and emission systems or testing facilities require accurate measurement of mass airflows greater than 3,000 kilograms per hour.
It would be advantageous to provide an improved mass airflow measurement system or device which can be employed on large internal combustion engines. It would also be advantageous to provide a mass airflow sensor which accommodates turbulent airflow caused by devices located immediately upstream from the sensor, such as elbows, remote air cleaners, superchargers, and other upstream structures in the air intake section of the engine which contribute to turbulent airflow.
Mass airflow sensors for use on internal combustion engines are produced by several different manufacturers, including e.g. Hitachi Automotive Systems, Bosch, and Siemens among others. Such mass airflow sensors are each sized somewhat differently from one another. Thus, different housings are currently needed for each such mass airflow sensor. It would be advantageous to provide a single airflow measuring housing which can accommodate the mass airflow sensors of many different manufacturers and would provide accurate readings, even when employed with large internal combustion engines.